Hello, just found this neat site today.
Anyway, something odd happened to my small cardon cactus. I had put it outside for a few hours and when I took it back inside it had these black spots at the top that I'm pretty sure weren't there earlier.
Did it get sunburned? Or is that from overwatering? I had watered it when I had it outside. So did it get sunburn and overwatering? I water it every few weeks, but maybe it needs less? This is the cardon after I took it back inside. I can try and get a better photo if needed.

to the forum!

I would like to invite @mcvansoest to the conversation.

Just a quick note about light and cacti ... I don't know if this is a plant you've had for a while or if it's relatively new, but full strength outdoor sun is very different from indoor sun, or whatever relatively protected (eg. greenhouse) situation the plant was in before the point of sale. It can be sort of dangerous to move plants right into midday sun from a more protected situation, whatever the case may be.

So generally I try to discourage people from treating indoor sun and outdoor sun as equivalent for their cacti (which they are not), and I try to discourage giving maximum exposure to newly acquired plants (that they are not used to). A position right inside the brightest window of the house would be ideal here, with a newly acquired (or otherwise indoor) plant.

The difference between indoor sun and outdoor sun mostly has to do with the way that regular window glass cuts out a lot of the UV part of the spectrum but allows the visible light to pass through. The UV in direct (outdoor) sun is what tends to threaten plants that haven't had some time and experience to get used to it.

Given what you have observed, find a nice bright but protected place for your cactus to recover. Avoid direct (outdoor) midday sun. Provide as much natural light as possible if this is an indoor situation. The more, the better indoors. If it's an outside plant, maybe filtered light or morning sun would be good for the near future. Go for the brightest location possible that doesn't include direct midday sun.

I can't say if what you observed has to do with sun, just trying to explain why that possibly that could be a factor.

Hi, thanks for the info and advice.
I've had it for a few months, its mostly been inside. It has been outside a few times before and has been fine. All that I can think of is that some water got dripped on the top, maybe it acted like a magnifying glass and burned it? Anyway I'll be back tomarrow.

I can not give any suggestion on the cactus..
Just want to @Cactusbat to the forum

I do not associate things going black with sun burn, I'd expect them to go bleached green, yellow, and then white, after which it is possible that rot sets in and things go black.

That does not happen in a few hours.

To help you better we need to know some more info: where are you located (rough location is enough). Are you growing it inside atm because it is not warm enough for the plant to be outside?

I have two good sized cardons which I grow in my front yard here in the Phoenix area, they take all day summer sun, with some sun stress but no sunburn, so while a sudden transition from inside to outside might cause sun burn, I would not expect things to go black.

So I would worry that for one reason the move outside caused an existing issue to become apparent. The kind of black I see on the plant I would associate with the onset of rot, which can be in response to high humidity in the indoor environment, or overwatering.

Hello @cactusbat I only encounter having blackened parts on my succulents if it got rained on and unable to dry out properly or exposed to sudden temp drop or cold draft which quickly causes black rot at the tip, similar to what your cactus shows.

@mcvansoest

I am in Chicago. The cactus has been mostly inside and only out on warm days. Thanks for the info.
When inside, the cactus is in a eastern facing window and has been watered only every two weeks.
@tarev
Now I'm suspecting that the cardon is a lot more sensitive to cooler temperatures and humidity then I thought. I'm thinking the water drops on it had something to do with it as thats where the black spots showed up.
Should I water it less and make sure not to get water on it?

If you are growing it mostly indoors, just water directly the media..not the entire plant, no misting..since the dynamics of inside conditions is way different than outdoors where there is faster dry out time, more sustained light and warmth.

Yes, sometimes there is just that cold draft that suddenly sneaks in and depending on the timing it can affect plants easily.

Also, when you water indoors, do it early in the day, not at night, so there is enough time for water to drain away and dry out.

Alright thanks.
Now do I have to do anything for it to help it heal or something?
Oh, I forgot to mention I have a small saguaro cactus thats been right next to it all the time and it has no black spots at all. I just find it surprising that the cardon is more sensitive.

The Saguaro is from Arizona where it can actually still get quite cold (nothing like where you are at, but still below freezing with wet and snow) in winter especially in the areas where the Saguaros grow (not in their complete region, but certainly in the higher reaches). Cardons are from much further south in Mexico and do not experience similar cool/cold weather with significant moisture.

On the rare occasions that I get at or below freezing weather in winter (one slight positive from the Phoenix heat island effect) I still try (it is getting harder because my biggest cardon is going on 8 ft tall) to cover the growth tips with some protection. I do not have to do that for the Saguaros.

However, both are not great long term indoor plants - aside from size considerations - unless you can provide a mostly warm fairly dry environment with lots of light throughout the year it is only a matter of time before more issues will arise. If these are to be indoors long term I would suggest finding a way to get them some grow lights - there are pretty decent ones available for not much money that do not actually look like they are grow lights.

Also the point Tarev makes is very good - avoid getting the plant wet when watering just water the soil, and I would reduce watering significantly as it get colder and darker (if you do not try and keep it in bright light with a warm environment) and I would also make sure there is significant airflow around the plants - which will help them dry faster and may stop things like this from setting in.

As to what to do now: keep the plant warm and dry, in bright light, with good airflow and hope it does not spread. If it does not spread it will likely scar the plant some, but it should keep growing. If it does spread your are SOL, cardons and saguaros do not deal well with getting their growth points cut off.
You will see the spots get larger and mushy.

The few times I have had minor cold damage on one of my Cardons, it did the black thing, but then kept on growing I could see for quite a while where that are was but would not be able to pick it out on the plant now, but it was many years ago.

Alright thanks.
I'll keep that in mind and keep an eye on it. As for grow lights and such I can do that.

I did not see the bottom part/container part of your plant, so I hope you are using containers with drain holes and your media is porous and well draining too.

tarev said: I did not see the bottom part/container part of your plant, so I hope you are using containers with drain holes and your media is porous and well draining too.

Its a plastic container, but it does have drain holes and a pretty light soil.




The surface is covered with small rocks. Thats my saguaro next to the cardon.
I actually got these from a website called planetdesert.
Anyway, the black spots seem to have dried up, they have not expanded.

The spots drying up is a good sign. I think it is too late in your season to transplant them, but come spring when they can maybe go outside for a while I would probably transplant them.

You will definitely want to find a way to get them more light. Looks like the window has a screen so for what these cacti normally like/need you are very much on the low end of the light spectrum.

Cactusbat said: Its a plastic container, but it does have drain holes and a pretty light soil.




The surface is covered with small rocks. Thats my saguaro next to the cardon.
I actually got these from a website called planetdesert.
Anyway, the black spots seem to have dried up, they have not expanded.

Ah that is good it has dried up and did not spread. As it dries up think of it as its 'battle scars'..a good survivor!